Abstract

Multichannel Fourier transform interferometry to measure the spectrum of arbitrarily short pulses and of fast time-varying signals was achieved using a micro/nanomanufactured multimirror array. We describe the performance of a demonstrator FTIR that works in the mid-infrared (MIR) range of 700-1400 cm−1 and reaches a spectral resolution of 10 cm−1 taking into account apodization. Spectral measurements down to pulse lengths of 319 µs were carried out using a mechanical camera shutter. Arbitrarily short pulses are expected feasible provided the source can deliver enough photons to overcome the noise equivalent number of photons.

Figures (3)

(a) Multimirror array (MMA) with a chess-board-like area of stepped planes that represent the bottom mirrors and a multitude of lamellae the top ridges of which embody the top mirrors (left). Denomination of angles (right): k wave vector of incident plane wave, γ the angle between k and its projection onto the x-z plane, φ the angle between the projection of k onto the x-z plane and the x axis. (b) Extract of simulated and measured interferograms for a spectrum produced by a narrow bandpass filter centered at 961 cm−1 for a Gaussian transmission peak of spectral beam-width (FHWM) of 20 cm−1. (c) Optical layout of MC-FTIR. Mirrors M2 and M3 can be optionally removed. (d) Experimental set up of the MC-FTIR. Image width 50 cm.

(a) Comparison of normalized spectra of a narrow bandpass filter taken with the IFS 66 interferometer over 60 s (solid line) and MC-FTIR taken at 20 ms (dashed line). (b) Shape of measured spectrum versus exposure duration ranging from 31.48 ms to 320 µs. Spectra are shifted vertically for better viewing. For all measurements, the pulse duration was reproducible within a tolerance of 20 µs.